Tank nozzle loads by API650

Hi,
Nozzle loads can be calculated in CAESAR using API650 input for large diameter tank. It is noticed that the nozzle loads are much higher if displacement vector D1 is specified in API650 input for radial deflection and nozzle rotation. The load case for this would be W+T1+P1+D1.
If vector D1 is left out in API650 nozzle flexibility calculation then the nozzle loads calculated by CAESAR in load case W+T1+P1 would be much lower than W+T1+P1+D1.

Please advise which load case is to be used for nozzle load input to API650 APPENDIX P for checking tank nozzle loads compliance?

Your help and advice would be much appreciated.

Thanks

The values in the displacement vector (D1) are determined from the API-650 equations based on the temperature, fluid head, and material of the tank. (This deflection calculation is separate from the nozzle stiffness determination.)

If your operation condition is such that "D1" always exists with "T1", then yes you should include "D1" in the load case.

Hi,
I've got a question about D1. Do we need to read "Radial Deflection Due to Fluid & Temp" and "Longitudinal Rotation Due to Fluid & Temp" from Errors and Warning, then return to input and define D1 or Caesar II automatically assigned those deflection to D1 and only we need to added to Loadcases?

Thanks in advance for advice.

Hi Richard,

Please expalin if the D1 Calculated by CII (if selected in API650 Nozzle)is included the thermal expansion/displacementof tank (radial and vertical) at nozzle junction. Or it is just for the shell deflection/rotation due to tank bulging effect?

Regards,
SCJ558

Early versions of c2 just computed those values, and you had to manually include them in the input. As of v.5.30, at the bottom of the API-650 input dialog there is a "drop list" where you can specify which displacement vector you want these values included in.

If you select "D1" for instance, you can see the displacements in the input (at the specified node) after the first Error Check. The reason you would want to include these deflections in your analysis is because this nozzle movement does move the attached piping (filtered by the nozzle stiffnesses of course).

Hi Richard,

I just don't get it. You said that previous versions of CAESAR II, we need to manually include those values in the input. But with v.5.30 after using the drop down list "D1", we can see displacement in the input at the specified node after the first Error Check. Meaning to say it should automatically tick the vector interface in the inputs with its calculated displacements as "D1".

Also "D1" is only deflection due to bulging right? So we need to have separate inputs for the displacement due to thermal expansion.

Please clarify.

Best Regards

The API-650 computation includes the deflection due to thermal expansion.

Yes, after the Error Check pass, if you go back to that nozzle node, you should see the displacements.

That is not what I get. After selecting D1 in the Nozzle flex input, I still need to enter the displacement manually. Otherwise, D1 does not show in the input window nor the load cases definition window. I am using CAESAR 2013.

Open a Support Request on SmartSupport and request someone to hold an on-line meeting with you.

I could not open a support request. Some thing is wrong with the website. However, I did some trial and errors; I found that CAESAR does indeed automatically create a displacement vector based on the API650 calculations. This works only and only if the nozzle element is not connected to a tank model via CNode. So, I will get a displacement vector for the radial displacement and nozzle rotation due to radial thermal expansion and pressure only.

In my case, I have modeled the tank as a piping element that is supported by an anchor at the base and a displacement vector for the settlement (Element 10-20). Then a rigid element without weight from the center of the tank to the tank wall node (Element 20-30). Then a nozzle element at which the nozzle flexibility is defined (Element "31"-40). On the nozzle element the nozzle node is 31 and the tank node (optional) is 30. In this case Caesar does not produce a displacement vector.

My way around that is "not" to choose a displacement vector from the drop down menu, run the error checker and write down the API650 calculated displacement and rotation, conduct a complete run and write down the displacement due to vertical thermal expansion (usually very small for tanks) and settlement, and finally go back to the input and manually set up a displacement vector for both API650, vertical expansion, and settlement. It is obviously very inconvenient, confusing and increases the possibilities of human error.

My question is, is there a better way that will actually make use of Caesar new API650 displacement vector automatic definition feature?

Unfortunately "no", because you're mixing apples and oranges.

The API650 computation for radial deflection and longitudinal rotation are based on the behavior of the tank shell. If you model that dummy rigid from the centerline to the nozzle, c2 will determine the expansion (thermal strain), which is also a radial deflection. c2 can't determine the longitudinal rotation because only beam elements are used.

So now you have two different radial deflection values - which one to use?

This is why if you connect the nozzle to another (2nd) element, the API650 deflection and rotation are not automatically applied.

Hello Richard,

After checking the thread, for me wasn't clear if the vertical displacement of the tank was considered or not by API 650 module.

I did some trial and error runs and did find out that during error check CAESAR only calculate the radial deflection and the longitudinal rotation and saw that after first Error Check, the input vector D1 reflect that writing dy=0.0 mm(vertical displ).

Also compare both methods:
1. Rigids to model the tank with Cnode at nozzle, inputting the displacement vector manually, D1 for deflections at the nozzle(radial deflection and rotation from API650 but vertical displacement "dy" blank to consider tank vertical expansion due to the expansion from the rigid that simulates the center of the tank) and D9 for settlement at the center of the tank.

2. Using API-650 and at the bottom of the input dialog in "drop list" selecting "D1" for the displacements in the input (at the specified node), but there is no vertical displacement calculated by CAESAR. And also input D9 for settlement at the nozzle node.

Why CEASAR discard the vertical expansion of the tank??
Which model you consider more accurate??

Thanks,

If you have the tank elements at temperature, the thermal growth (vertically) will be included. API-650 provides equations for only the radial deflection and longitudinal rotation.

Hi Richard,

I am using CAESAR 2013.I can not see the "D1" (Bulging defection Calculated by CII automatically)after Error checking although i didn't model tank body.

any comments?

On the API-650 dialog (where you define the Tank data), at the very bottom is a drop list control that allows you to specify which displacement vector you want the computed "bulge" data to be applied to. Make sure you set that value.

yes, I did select "Set Displacement Vector" as "D1", however, i can not see the related bulge deflection is shown in the main input menu.

my CII model:

node 20~29, tank rigid no weight, anchor node20
node 30~32, tank nozzle node30, tank node29......set displacement vector:D1

I even delete the tank no weight rigid element(node20~29), but it still doesn't work.

who can give me shout? thanks a lot

Open a Support Request on Smart Support and send in your c2 model.

I have two concerns about modelling and dealing with tank nozzles:

1. The displacements that are calculated by Caesar II according to API 650 due to the bulging effect are the "unrestrained" displacements. Since the nozzle will be connected to a piping system that has its own flexibility and weight and thermal effects on the nozzle, I think imposing those calculated "unrestrained" nozzle displacements to the whole system is not the true case and not correct.

2. Imposing the "unrestrained" tank nozzle displacements at the nozzle will cancel the nozzle flexibility resulting in very high loads which are not true, and that is what I got after a trial run.

My understanding, is that there is no way to get "near" true loads and displacements on the nozzle but to model the tank elements to account for the vertical and radial thermal growth, and completely ignore the "unrestrained" shell rotation, as imposing those displacements on the tank nozzle will cancel the shell flexibility out of the analysis and result in unrealistic very high nozzle loads.

Please correct me if I am missing anything.

You could be correct in your conclusion regarding the accuracy of the "unrestrained" displacement/rotation.

The displacements will not cancel the flexibilities, because the nozzle and pipe are connected with a CNODE. The Nozzle is displaced, but the flexibilities are between the nozzle and the pipe. The pipe node and the nozzle node may see different deflections based on the "stiffness-load" values.

Even modeling the tank (which I recommend) won't help with the bulging, since c2 uses 3d Beam elements. There is no accounting for shell behavior.